1. Field of the Invention
The present invention relates to the formation of adhesive coatings on moving objects and particularly to the application of an evenly dispersed layer of glue to a surface of a book block so as to enable the subsequent fixation of a backing material or the like. More specifically, this invention is directed to a process for depositing an evenly dispersed film of glue on the back of a book block, or any other similar article, with the aid of an applying roller. Accordingly, the general objects of the present invention are to provide novel and improved methods of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention will be described in connection with the application of glue to pre-formed book blocks which are being transported at a substantially constant speed by a linear conveyor system. It is well known in the art to employ a rotating application roller to transfer a film of glue to a book block so as to enable the subsequent affixation of paper to the back of the block or the fixing of a headband strip to the top and bottom of the block. Typically, the application roller will receive the glue which is to be subsequently transferred to the book block from a "dip and dosing" roller which runs in a reservoir containing glue, the roller contacting the surface of the glue. Thus, the applying roller will receive a film of glue from the dip and dosing roller and will transfer this film onto the moving book block. The applying roller is customarily moveable inwardly and outwardly in synchronism with the book block conveying system to cause the engagement and disengagement of the applying roller with the moving blocks. It is also known in the art to contour the applying roller, which may be fabricated from rubber, so that it is generally complimentary in shape to the back of the book block.
The prior art techniques for forming a film of glue on a moving book block have been characterized by two long-standing problems. These problems, which will be discussed in more detail below, include the inability to reliably and uniformly coat the entire surface which is to be covered with a film of the adhesive. The second problem has been the deposit of an excess of adhesive at the leading and/or trailing edges of the surface to be coated thus leading to the unacceptable application of glue to the cut edges of the sheets forming the book block. In either case, i.e., an incomplete gluing of the cover or a resulting "dirty" book block, the product must be rejected.
Regarding the first of the above-discussed problems, it is not possible to obtain precise conformity of the profile of the glue application roller to the shape of the back of the book block to which the film of adhesive is to be applied. In the first place, since the book blocks are comprised of paper, the size and shape thereof cannot be maintained within close tolerance. Secondly, since the same production equipment is employed for the manufacture of many different books, the cost of providing and storing an application roller for each different book block configuration would be prohibitive. Accordingly, since it is not practical and/or not possible to provide a profiled glue application roller which exactly fits the shape of the back of the book block to which the film of glue is to be applied, a complete coating with adhesive of the area on the book block to which the covering is to be affixed could not previously be obtained. In this regard, it is to be noted that when a roller having a profile which is flat relative to the back of the book block is employed, a film of glue having a generally parabolic shape is deposited. Accordingly, the corner areas of the back of the book block do not receive any glue. Conversely, if the curvature of a profiled glue application roller is greater than that of the book block, the middle area of the book block back will not receive any glue. In either case, inadequate gluing results from the fact that the profile of the application roller does not have time to adjust to the contour of the moving book block.
In an effort to overcome the above-discussed problem of inadequate gluing, it is known to position the applying roller so that it is awaiting arrival of the block, the roller subsequently moving with the block. This technique has the disadvantage that an excess of glue will be deposited on the front cut edge of the book block when that edge is engaged by the roller. This problem is magnified by the fact that the surface areas within the concave profile of the roller travel at different speeds, which are a function of roller circumference, relative to the book block. Typically, the applying roller will be caused to rotate at a "nominal" speed such that a point on its average circumference is travelling at a velocity which is slightly lower than the linear velocity of the book block. This results in the velocity of the middle, i.e., central or minimum diameter region of the roller being less than the linear speed of the book block. This speed differential, in turn, favors the deposition of excess glue at the cut edge.